Furnace control



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Nov. 115 1924- L. J. HESS ET AL FURNACE CONTROL Filed April 26, 1919 5 Sheetr.$hest 1 BEST AVAlLABLE COP.

N 11, 1924. r L. J. HESS ET AL FURNACE CONTROL Filed April 26, 1919 3 shems sheet 2 WITNESSES BEST AVAXLABLE COP.

Nov. 11, 1 24. 4 1,515,044-

L.- J. HESS ET- AL FURNACE CONTROL F'iledmpril 26. 1919. a'sheets' sheet. 5

mVEN'ToR a M M 4 I MW W- W' Patented Nov. 11, 1924.

UNITED STATES PATENT OFFICE;

LAWRENCE J. HESS, OF YOUNGSTOWN, AND IJERRILL G. BENJAMIN, 0F POLAND, OHIO, ASSIGNORS TO THE BENJAMIN ENGINEERING COMPANY, OF CLEVELAND, OHIO, A

CORPORATION OF OHIO.

FURNACE CONTROL. w 3, 3 '3 Application filed April 26,

To all whom it may concern .7

Be it known that we, LAWRENCE J. HESS and Mi-ziuuu, G. BENJAMIN, both citizens of the United States, residing at Youngs town, county of Mahoning, State of Ohio, and at Poland, county of Mahoning, State of Ohio, respectively, have invented a new and useful Improvement in Furnace Control, of which the following is a full. clear, and exact description, reference being had to the accompanying drawings, forming part of this specification, in which- 1'? Figure l'is a diagrammatic view showing the invention as embodied in the control for a. steam boiler furnace.

"Figure 2 is a similar view showing a mo dification. i

Figure 3 is a view similar to Figure 1 but showing the invention as applied to a bat te of boilers. f f f n our co-pending application serial No. 463,675, filed April 22, 1921, as a continua tion in part of the present application, the broader features of our invention have been more clearly described and claimed, the present application relating particularly to the control of the furnace draft and furnace pressure.

The present invention relates to furnace control. One feature of the invention relates to an automatic control of the furnace auxiliaries such'as the drafts and stoker. Other features 'ofthe invention relate to the control of such furnace auxiliaries in accordance with the demand for'steam'in the case of a 'boilerfurnace. Another feature ofthe invention relates to the control of the gas pressure in the combustion chamber of the furnace so as to progressively'vary such con trol for varying rates of combustion, Another feature of the invention relates to the electrical means hereinafter described for effectingthe furnace control. Still other features of the invention relate to certain combinations and arrangements of parts hereinafter described, and particularly ointed out in the claims, the advantages of which will be apparent to those skilled in the art from the following description Referring first to the embodiment of the invention illustrated in Figure 1 :A steam boiler indicated generally by reference numeral 2 and its furnace by reference 1919. Serial No. 292,954.

numeral 3. A plurality of such boilers and theirfurnaces is preferably employed, the steam from such battery of boilers being collected in a common steam pipe or header 4, which, as shown in Figure 2,-exte ndsrat right angles to the plane of the paper over a plurality of boilers. p The boiler furnace is provided with a forced draftblower 10 which delivers the forced draft to the ash pit 11 .under. the grate 12. The forcedE'draft fan is'driven by an electriomotor 13, The wastdgas flue 14: is provided with: an inducedfdralft fan 15 driven by a motor 16.;-,This waste gas flue, is also provided ,with afdamperQT which is opened orjclosed bydnean's been electric motor 18 connected with'thei'dainper 1"! by means o f a worm" gear} 19. The furme is also'f,providd'withfan5.J?- 1Qm?' i Stoker indicated generally by ,.refe'1 "ence numeral 2Q, which is driven by'fan'electric motor 21. 7 draft fan, the "damper and"the Stoker are duplicated for each of the boiler furnaes'bf the battery.

The boiler namely, the draft producing and means and the stoker, p h trolled accordance with the-dema d steam on the .1 oz: auxiliaries aboye' jde scribe d. re la i boiler or battery bff'b'oilrsso as to m intai'n-the output bffth'e boileror boilers equa'l to the demand and thereby maintain a substantially constant/steam pressure at the same time maintaining the most efficient furnace" conditionsfor its d e,-' mand. When there, is a. greater'demandfQr steam,- the steam pressure ofourse will drop. This'drop in steam pressureoperates through the-control, 'now to be described to automatically increase the feed off iel by the Stoker and to siinultaneously arfd aii tof matically increase the furnace 'draffifso that the boiler furnaces are trolled to assume the increased load? Silill: larly, if the demand for steam decreases, the control operates automatically 'tocaus'e the stoker to feed less fuel to the'firejiand also to cause the draft fansand damper to decrease the draft through the-furnace;

The control is an electric control'and in eludes a motor generator'set, indicated generally by reference numeral 25; the speed of which is controlled in accordance with the Theff orced draft fanffthe indiiceld automatically con wits-r LABLE CQ demand for steam in the boiler by means of a steam pressure actuated regulator26. The forced draft =motor =13, the induced drafi motor 16, and the stoker motor 21, are all connected so that their speed varies in accordance with the speed of the motor generator set 25. The motor which opens and closes the damper 17 is connected so that it is controlled both by the motor generator set. and also by a compensator device which in turn is controlled by the pressure of the gases in the combustion chamber of the furnace.

The motor 2? of the motor generator set 23 is supplied with current from the current mains 28 and' 2 9, which are preferably the usual direct current mains as employed in factories. The armature of the motor 27 is supplied directly from the .mains 28 and 29. The field 30 of the motor 27 is connected through an adj ust-able rheostat 31 which has a movable contact arm 32. The contact 32 is connected .withthe arm v33 of the regulator 26.: The regulator 26 is connected through a pipe 34 to a steam header 4 of the battery of boilers. Theoperation ofthe regulator '26 is, such that when the demand e la am de re s s idt ste m p e u onseeuen y r e ab v a p det rmin d point, the arm 33 israised to raise the contact 32 and thereby decrease the resistance inseries with the motor fieldQB O, thereby Idecreasmg thelspeed ofthe motor. Conversely, whenthe demand for steam increases and the steam pressure consequently falls, the tarm 33 lowers :thecontact 32- thereby inserting more resistance in series with the motor field, 30-and increasing the speed of the jmotor generator set.

The regulator 26 18 preferably one which has a graduated step by step movement, the arm 33 assuming a number of intermediate positions in accordance with the. variations inthesteam pressure. Such regulators are old and well known in the art. Examples of such regulators in the patent literature are the Spencer Patents Nos. 338,686 of March 23, 1886 and 479,854 of August 2, 1892. A number of such regulators are on the. market such as the well known Spencer regulator, bfason regulator, etc., so that the construction of the regulator need not be described in detail as its construction and operation will be readily understood by any one skilled in the-art.

-Whilezit is preferred to control the furnace in accordance with-the demand for steam by meansof :a regulator actuated by the steam pressure, other devices responsive to theazariations in the demand for steam may be employed. Forexample, a steam flow meter may interposed in the main steam line. from-the boiler or-battery-of boilers, and so connected with the electrical' system that the speecl of the-motor-generator set will increase or decrease as the How of steam. in creases or decreases, respectively.

The showing in the drawings of the electrical connections is diagrammatic. It is to be understood, of course, that the motor generator set is to be provided with the usual switches, rheostats,'fuses, etc, as to be readily understood by anyone skilled in the art.

The generator 40 of the motor generator set is mounted on the common shaft with the motor 27 to be driven thereby, as will be readily understood by one skilled in, this art. The field 41 of the generator is connected across the feed mains and 29 through a manually adjustable rl 1e ostat 42 which may be adjusted to vary the voltage of the generator, 40. The generator .40. supplies the auxiliary feed wires43 and 44. The forced draft motor 13 .has its field .45 connected acrossthe main feeder lines 28 and 29 so that the .motor .field has constant excitation. The armature. of the; motor ,13 is connected acrossthe motor generator feeder lines 43 and 44 toreceiye variable. voltagefrom the motor generator set. fi s-will .be readily apparent, when cthe speed of. the motor generator set increases, thevolta .on the lines 43 and 44 also increases an the speed of the forced draft motor- 13 will correspondingly increase and increase .the forced draft. The manually operable .rheostat 46 is inserted in series with the field 45 of the motor 1350 that the speed of-such motor maybe adjusted. suchadjustment would be made, for example, if it were found that-the forced draft fan-was either too weak or .too strong for the induced draft, or if the forced draft ,fan for one boiler furnace was weaker or stronger than the forced draft fan for the other boiler furnaces in the battery. Once-the rhe-ostat 46 has been adjusted, it requires little, if any, further adjustment, the control of the forced draft fan in accordance with :the boiler pressure, being had entirely by mea-ns of the automatic electric control.

The armature of the induced fan draft 1G is similarly connected across the variable voltage feeder lines 43 and 44 from the 2;

motor generator set 25, and its field 47 is connected in series'with a manually adjustable rheostat 48 across the constant voltage main feeder lines 28 and 29-. The-Stoker motor 21 similarly has its armature connected across the motor generator feeder lines 43 and 44 and has its field-49connected through a manually adjustable rheostat 50 across the constant voltage main feeder lines 28 and 29.

The main feeder lines 28 and 293and the auxiliary feeder lines 43 and'44 are shown broken off at the left hand side of Figure -1.

It is to be understood, however, that such feeder lines are continued to the auxiliaries ill) BEST AVAILABLE COP.

of the next boiler furnace, etc., such feeder lines supplying the various motors for all of the boiler furnaces in the battery.

A single motor generator set and its steam actuated controller 26 thereby controls the feed of fuel and rate of combustion for the furnaces of an entire battery.

As will be readily understood from the foregoing description, if the steam pressure in the header 4'rises, 'the arm 33 and contact 32 of the rheostat will be raised a corresponding amount," thereby 1 reducing the resistance in series with the field of the motor 27 and reducing the speed of the motor generator set. This reduces the voltage on the lines 43 and 44f an d cor-' respondingly decreases the jfspeed 'of the draft fan motors and the stoker motors, thereby decreasing the amount of fuel feed to the fires andthe amount o fj air supply to the fires to supportfcon bustion. Similar ly, if the steam pressure falls, the'inotor generator set is speeded up, therebyQspeeding up the draft fan motors; and stolrer motors and supplyingrnoreicoal and air to the furnaces to carry thejncreased load. Since the regulator 26: assumes intermedi ate positions in accordance with the steam pressure, the speedof the nfotor generator set will be similarlyg 'afi'ected so 'that if the demand for steam "becomes stabilized, the motor generator] set and the fsevera ltmotors for the furnace auxiliaries will assume the correct speed toimaintain 'the fires at the point to just carry th boiler load The entire system of draft" motors and, jstoker motors may be regulated bymeans'fof the hand rheostat 42 which controls the" field and, consequently, "the voltage of the generator 40. The individual 'n'iotorsmay have their speed adjusted by mea'nsflo'fthe rheostats 46, 48. and 50,"on e, of these rheostats being provided for eachmotor in the entire battery. By means ofthese ,rheostats the forced and induced drafts and the stokers of each furnace'may be correlated with each other and also the feed of fuel and rate of combustion of the several furnaces may be correlated. This manual ad justment by means of which thefeed of fuel or the draft of one furnace may be adjusted or varied with relation to anotherjfurnace, does not interfere with the automatic control of the electrical systembymeansof which the draftand fuel feed of all of the furnaces are simultaneouslycontrolled. In other words, the manualad justment of the rheostats 46, '48 and will adjust the draft and fuel feed of one furnace with relation to that of the other'furnaces' in the battery. while the automatic regulation by means of the Comniohinotor generator set 25 varies the rate of combustion and feed of fuel of all thetfurnaces in' accordance with the steam'pressure. 'The common control system serves to equalize the load upon the several boiler furnaces This equalization of the load results in the most eflicient operation of the battery. Since each boiler can be made to always carry its shareof the total load, a greater 'loadcan be carried with a given number of boilers than is the case Where some boilers carrydess than their proper share of thexload. .It is well known that boilers operated continuously at moderate ratings show better efliciency than boilers operated atf'variable ratings froinlloiv to very high. The life of the furnace brickworlr'and other partsis greater under the conditions of constant load than otherwi'se; By providing the means for equalizing the load onallthe furnaces, we reduce the variations in rating at which the individual boilers are operated to the actual variation" in the; station load,. thus causingiarninimum fluctuation in the 'ratf ing' of any: individual boiler furnace.

The draft damper 17 is controlled to open and 'tliereby j inorease the draft when the steam pressure falls' and to "close'j'and de crease thesdraft when the steam pressure rises." The opening and" closing of this damper is so correlated with the forced and induced draft fans and withj the chimney draft," if, any, that the pressure of the gases in; the 4 combustion chamber of the' furnace progressively decreases" as the rate of coin: bustion' increases. 'To'eifect this correlation, the armature 18 is connected with'areversing switch' indicated generally by reference character '60,:'sothat..the motor 18.n1ay be driven either forwardor'baclrward toopen or close th'e' damper'f 17 through the worm gear 19. 'TlieTfield 61 of the motor 1 8is constantly excited andv is connected"across the main feeder lines 28"and 29. The reversing switch comprises cross connected contacts 62and 68, which are connected to the lead 64 of the'motor 1,8 and cross-connected'contacts 65 and 66, which are connected with the lead'67 of the motor 18. Arranged'to make contact with the fixed contacts are twomovable contacts 68 and 69 which are connected with the main feeder leads 28 and 29, respectively.

The fixed contacts are carried on a plate 70 which is preferably immersed infthe oil in the oil tank. 71 to prevent arcing. This plate 70 is longitudinally moved by means of an inclined cam 72, which'works in fixed guides'and ismoved up and down by means of the plunger 73'of "the solenoid 74. The plunger 73 is drawn upwardly by the solenoid against the pressure of a spring 75. which is adjusted'by means of adjusting screw 76. The solenoid 74 is ,connected across the feeder' lines from the motor gen-' erato'r set 25. When themotor generator set speeds upand its line voltage is thereby increased; the plunger 73 is correspondingly BEST AVAILABLE COP.

drawn upwardly and the cam 72 shifts the contact carrying the plate 70 to the right, as viewed in Figure 1. The movable contacts 68 and 69 are carried on the lower end of a hell crank 80, the horizontal or upper arm of which rests against a knife edge 81, carried by a hollow downwardly opening bell or float 82. This hell or float 82 floats on the surface of a liquid, preferably oil,

l in the tank 71. The bell orfloat is free to move up and .down beingguidcd by the guide 83. The upward or downward movement ofthe bell 82 is caused by the varying pressure of the air or gases therein. Opening inside of the bell 82 is a pipe 84:, the other end of which opens into the combustion chamber 85 of the boiler furnace. lYhen the pressure of the gases in the com bustion chamber increases, the pressure is communi,cated-to..,theinside, of the bell 8 2 which rises, therebymoving the movable contacts 68 and 69,to the-left, as shown in Figure 1. 1 If the pressure. of the gases in the combustion chamber falls, the bell 82 drops and the movable contacts 68 and 69 of the reversing switch are moved to the right as viewed in Eigure 1. The bell 82 serves, as a compensator and, .co-operates with the electrically-controlled solenoid74c so that, ,the draft as maintained by the damper 17 is dependent .upon. two functions of the furnace, na ely, .the. boiler pressure and the pressure of the gases of combustion in the furnace. p

The expression function of the furnaces as used herein, and particularly in the claims, isnot intended to lee-limited to any one function butto include the steam pressure, the pressure of the gases in the combustion chamber, or any other. function in accordance with which itis desired to control the furnace.

The operation of .the damper control is as. follows: Sup-pose that an extra demand for steam comes on the boilers and the steam pressure begins to drop. The regulator 26 operates to speed up the motor generator set thereby increasin the speed of the forced draft fan, the inc uced draft *1 fan, and the stoker feed. The solenoid 74 raises the plunger ,73, moving the contact carrying plate to the right. Simultaneously the increased forced draft increases the pressure in thecombustion chamber of 1 the furnace and thereby raises the bell 82,

maintain a substantially constant pressure of the gases in the combustion chamber for any and all rates of combustion. The action of the solenoid 7& through the cam 72, however, prevents such a constant pressure 7 maintenance and causes the pressure in the combustion chamber to vary with the rate of combustion. As shown in the drawings, the solenoid 74: will operate to decrease the pressure in the combustion chamber of the furnace as the, rate of combustion increases, and this is the condition which it is desirable to maintain, particularly with a stoker fired furnace of the type now commonly in use in which We find it advantageous to lower the combustion chamber pres sure (or increase the draft over the fire) as the rate of combustion increases. It will be seen, therefore, that the ultimate effect of the. automatic regulating system herein disclosed, is to increase the draft and fuel feed in accordance with the demand for steam, and thereby automatically maintain a substantially constant steam pressure, and also to so control the pressure of the gases in the'furnace that there is an increased draft over the fire (decreased pressure in the combustion chamber) as the rate of com.- bustion increases.

v The damper 17 may be -manually controlled if desired. For this purpose a doublethrow switch is inserted, in, the leads of the motor 18,'by means of which the motor may be disconnected from the automatic reversing switch 60,,and connected with a manual reversing switch 91. By throwing the manual reversing switch 91, the operator may open or close the damper.

In Figure 2 is illustrated a modification. The operation of the system is essentially the same as that shown in Figure 1, the only essential difference beingthe control of the forced draft motors, the induced draft motors and the stoker motors, by means of varying their fields, instead of varying the Voltage supply to their armatures.

Referring to Figure 2:The unmimbered parts all have the same construction and mode of operation as those shown in Figure 1. The motor generator 25 has its speed controlled by means of the steam actuated regulator 26, as described in connection with Figure 1.

Referring first to the motor 13 for the forced draft fan. This motor has its armature connected directly across the constant voltage main feeder lines 28 and 29. The motor hastwo. fields and 101. The main field 100 is. connected across the constant voltage main feeder lines 28 and 29 through a manually adjustable rheostat 46. The auxiliary field 101, is the weaker and is arranged to. buck the main field 100. The auxiliary field 101 is connected across the variable voltage feed lines43 and 4A, which llU BEST AVNLABLE 00? are supplied with the variable speed motor generator set 25. As the speed of the motor generator set increases upon a drop in steam pressure, as before described, the voltage on the lines 43 and 44. increases. This strengthens the auxiliary field 101 which bucks the main field 100 and thereby weakens the field of the motor 13. This causes the motor 13 to increase in speed and supply more air to the furnace.

Similarly, the induced draft fan motor 16 has two fields, the main field 102, which is connected across the main feeder lines 28 and 29 and a bucking auxiliary field 103 connected across the variable voltage lines 43 and' i l so that when the speed of the motor generator set increases, the speed of the induced draft fan correspondingly increases.

In the same way, the stoker motor 21 is provided withtwo fields 104i and 105, the

field .104 servin as the main constant voltage field and tie field 105 has a bucking variable voltage field, such fields operating to increasethe speed of the stoker motor in accordance with the increase of the speed of the motor generator set 25.

V The invention has been set forth in this application as applied to a steam boiler and furnace, butit will be understood that it is equally applicable to boilers utilizing liquids othertlian 'water as, for example, the recently developed mercury boiler. V

While'the'inventionis illustrated as embodied in a coal fired furnace in which the fuel feed is automatically regulated by varying the speed of the stoker motor, it will be obvious that the fuel feed may be automatically regulated when other fuels, such as gas oil or pulverized coal, are used. For exam e, in using gas the gas supply may be sultably throttled, or in case the gas is supplied by a gas producer, the fuel feed may be varied by varying the speed of the blower supplying air to the gas producer. The term furnace as used in the claims, unless otherwise expressly limited therein, is intended as a word of general description and not of limitation, and to include any apparatus which is supplied with fuel and air and in which combustion takes place. For example, the term furnace, when used broadly herein, is intended to include a gas producer which is supplied with fuel and air and in which gas is produced by incomplete combustion. The rate of combustion and fuel feed may be automatically controlled in accordance with the demand for gas, or the gas pressure (corresponding to steam pressure in a steam boiler furnace), or other function of a gas producer type of furnace.

For the sake of simplicity the drawings have been made largely diagrammatic. It is to be understood that the invention is. not

limited to its preferred embodimentv but that the various instrumentalities diagrammatically illustrated may be variously 'constructed and that theinvention may be em-.

bodied in other structures within the scope of the invention as defined in the'following' ing mechanisms,- one controlledl'in accord;

ance with the pressure 'of the l ase's in furnace? and tending to mairitaln an gate; lished pressure therein, and the otherfcdrif trolled in accordance witl jj the demand n the furnace and variabletherewithfforyary ing the pressure to.belmaintainedinfthe furnace, substantially as described,

3. The combination with a boiler anilits furnace, of draft-controllingifiietiis, and means for regulatin thejdraft control to vary the pressure OFthega esin'the fur}, nace, comprising two co-op'erating mocha-f nisms, one tending to maintaimthe'pressure of the gases substantially constant, and the other serving to progressively varyfhepressure of the gases in accordance with the pressure in the boiler or boiler connections, substantially as described. I fl 4:. The combination with a boiler and its furnace, of a regulator governed by both the pressure in the boiler or boiler connec tions and the pressure of the gases in the furnace, ,the regulator including means responsive to the pressure of the gases in the furnace for maintaining an established pressure therein, and means connected with the pressure in the boiler for establishing the pressure to be maintained in the furnace, said means being effective for causing graduated decrements in the pressure to be'mairitained in accordance with increments in the load carried by the boiler, substantially as described 5. The combination with a boiler and its furnace, of a regulator for controlling the pressure of the gases in the furnace, the regulator including means responsive to the pressure of the gases in the furnace and tending to maintain an established pressure therein, and the other being eflfective for establishing such pressure and serving to llO )ro ressivel decrease such establishedores- BEST AVAlLABLE COP;

6'. The combination with a battery of furnaces, of draft controlling means for each furnace, and means for regulating the draft control, comprising two co-operating mechanisms, one operated in accordance with the pressure of the gases in the individual furnace and tending to maintain an established pressure therein, and the other operated in accordance with a function of the entire battery and effective to establish the pressure of the gases to be maintained in the individual furnaces, substantially as described.

7. The combination with a battery of boilers and their furnaces, of draft controlling means for each furnace, and means for regulating the draft control, comprising two co-operating mechanisms, one controlled by the pressure of the gases in the individual furnace and tending to maintain an established pressure therein, and the other controlled in accordance with the demand on the battery to establish the pressure to be maintained by thefirst mentioned means, said last-mentioned means being effective to progressively vary the pressure to be maintained' as the demand is Varied,'substantially as described.

8; The combination with a battery of boilers and their furnaces, of draft-controlling means foreach furnace, and a regulatorfor such draft-controlling means, each regulator comprising twocooperating mechanisms, one controlled by the pressure of the gases in its furnace and tending to maintain an established pressure therein, and the other controlled in" accordance with the demand on the entire battery of boilers and serving to establish the pressure to be maintained by the first 'm'entioned' means, the last-mentioned means being effective to progressively decrease the pressure to be maintained as the demand on the battery increases, substantially as described.

9. Furnace control apparatus, including draft-regulating means, an electric motor for operating the same, relatively movable electriccontacts for controlling the motor,

4 means dependent on thep'ressure in the combustion chamber of the furnace for relatively moving the contacts, and means vary ing with the demand on the furnace for relatively moving'th'e contacts, substantially as described. T

10. Furnace control apparatus, including draft-regulating means, an electric motor for-operating the same, movable and rela tively stationary electric contacts for controlling the motor, means actuated by the gases in the furnace for moving amovable contact, and means for shifting the position of a co-operatin relatively stationary contact; the draft control motor being effective for changing the pressure of the gases in the furnace, whereby the means responsive to the gas pressure tends to maintain substantially constant a gas pressure determined by the position of the relatively stationary contact, substantially as described.

11. Furnace control apparatus, including draft regulating means, an electric motor for operating the same, movable and rela tively stationary contacts for the motor, a gasometer bell having a oressure connection with the combustion chamber of the furnace and being operatively connected with a movable contact, the gasome-ter bell being effective for moving such contact to operate the motor and maintain an established pressure in the furnace, and means for shifting a co-operating stationary contactto establish the pressure to be maintained, substantially as described.

12. Boiler furnace control apparatus, including draft-regulatin means, an electric motor for operating tie same, relativelymovable electric contacts for controlling the motor, means dependent on the pressure in the combustion chamber of the furnace for relatively moving the contacts, and means varying with the boilerpressure' for relatively moving the contacts, substantially as described.

13. The method of operating a furnace,

which includes automatically maintaining an established pressur in the combustion chamber of the furnace for a given demand on the furnace, and varying such established pressure with the demand, substantially as described. "14:. The method of operating a battery of furnaces, which includes automatically establishing in the combustion chambers of the individual furnaces'predetermined pressures varying with the demand on the bat te'ry, and automatically maintaining in each furnace of the battery the pressure estab lished for any particular demand, substantially as described.

15. The method of operating a boiler furnace, 'which' includes automatically establishing in the combustion chamber of the furnace a predetermined pressure varying with th boiler rating, and automatical ly maintaining the pressure so established, substantially as described.

16. The method of operating a battery of boiler furnaces, which includes automatically establishing in the combustion chamber of each furnace of the battery a. predetermined pressure varying with the steam pressure in the header of the battery, and automatically maintaining the furnace pressure so established, substantially as described.

17. Control apparatus for a battery of furnaces, including fuel supplying means, a stack damper for each of the furnaces, fuel-supplying control means adapted to BEST AVAILABLE coP control the fuel-supplying means for all the furnaces in the battery, damper control means adapted to control the stack dampers for all the furnaces in the battery, means responsive to a function of the battery operatively connected with both the control means and adapted to vary the same to increase or decrease the rate of fuel and air supply with Varying demands on the battery, and means for automatically controlling the stack damper of each furnace in the battery in accordance with a pressure condition of such furnace, substantially as described.

18. Control apparatus for a battery of furnaces, including fuel-supplying means, a stack damper for each of the furnaces, fuel-supplying control means adapted to control the fuel-supplying means for all the furnaces in the battery, damper control means adapted to control the stack dampers for all the furnaces in the battery, means -responsive to a function of the battery 0peratively connected with both the control means and adapted to vary the same to increase or decrease the rate of fuel and air supply with varying demands on the battery, means for manually varying the effect of variations of the function-responsive means on at least one or said control means, and means associated with each of the furnaces in the battery for controlling the stack damper of such furnace in accordance with a pressurecondition of the furnace, substantially as described.

In testimony whereof, we have hereunto set our hands.

LAWRENCE J. HESS. MERRILL G. BENJAMIN. 

